Experimental investigations have been carried out on permeable aprons consisting of stones enclosed in nets underlain by a Terzaghi Vicksburg layer (T-V filter layer) placed on the downstream side of a weir having different floor lengths. The effect of length of apron, depth of downstream pile and depth of tail water have been studied with a filter layer on scour pattern (with or without stones). The results indicate that the proposed apron underlain by a T-V layer acts as a good protection measure against scour, downstream of the weir. The length of impervious floor of the weir can be reduced by more than 50 percent by using this protection. Further, a higher exit gradient can be permitted without the fear of failure or piping in a weir. However, these stones enclosed in nets underlain by a filter layer may also find application in protection of slopes of overflow earth dams as well.
